The background information discussed below is presented to better illustrate the novelty and usefulness of the present invention. This background information is not admitted prior art.
Fluids may contain contaminants that are gaseous at normal atmospheric conditions, but which are also often mixed or dissolved in the liquid portion of that fluid. Volatile Organic Compounds (VOC) are one example of a group of such contaminants. Another example is the contaminant hydrogen sulfide (H2S) which may be present in water, crude oil or other hydrocarbon fluids. Hydrogen sulfide can be present naturally in well water and in crude oil, or it may be introduced into wastewater via industrial processes. Water and crude oil will be referred to as sour, if they contain substantial amounts of hydrogen sulfide.
Hydrogen sulfide is a colorless gas with the characteristic foul odor of rotten eggs. It is also very poisonous, corrosive, flammable, and explosive. The industry considers oil or water containing 100 parts per million (“ppm”) (0.01%) sulfur sour oil and sour water. Although this is the minimum level, oil wells and water can contain higher amounts. Oil and water can contain hydrogen sulfide up to 300,000 ppm (30%) at the immediate gas/liquid interphase, the vapor space in a tank or container, and the atmosphere surrounding a spill. At higher concentrations, hydrogen sulfide is toxic and deadly. It is therefore desirable to remove or to inactivate hydrogen sulfide contaminants.
A traditional method of removing or inactivating hydrogen sulfide from fluids such as crude oil or water is to use a chemical scavenger, for example 1,3,5-tri-(2-hydroxyethyl)-hexahydro-s-triazine (HHTT, CAS number 4719-04-4), usually simply referred to as triazine. This hydrogen sulfide scavenger reacts with the hydrogen sulfide converting it to a more non-volatile product, which may be then subsequently removed from the fluid being treated or simple left in solution. However even though these products are non-volatile or less toxic, it is often undesirable to leave scavenger end-products within the treated fluid (since the overall “sulfur” content has not been reduced, but has merely been converted to a less toxic form). Therefore additional steps may need to be taken to remove the scavenger end-products from the fluid, resulting in additional costs and more complex equipment.
Additionally, amine-based hydrogen sulfide scavengers are also known to form an unwanted dithiazine byproduct (particularly if the scavenger is “over-spent”). This byproduct material is also known as amorphous dithiazine, and appears to begin forming when triazine is around 60% spent. This amorphous dithiazine byproduct is exceptionally insoluble and substantial quantities can deposit throughout a fluid processing system. Dithiazine can form blockages in processing equipment, storage tanks, truck tanks and disposal wells. Cleanup procedures are time consuming and difficult. Often, the equipment has to be taken off-line so such deposits can be manually chipped away. The industry places much effort and incurs great cost in the prevention and treatment of dithiazine buildup.
Hydrogen sulfide treatment systems also often take the form of elaborate systems employing complex components such as packing, porous media or contact cells to increase surface areas and create tortuous fluid paths (e.g. to increase scavenger and contaminant interaction), fluid nozzles or distributors (e.g. to attempt to evenly distribute scavenger or contaminated fluid over the packing), demister pads (e.g. to remove contaminated liquid or scavenger droplets entrained in a vapor stream) and sparge-bars (e.g. to introduce a scavenger into the fluid). These elaborate systems typically are in the form of tall, upright vessels or towers, to increase the time that fluid or scavenger trickles downward through a deep layer of packing (or to increase the time that lighter fluids take to move up through a deep layer of contaminated fluid), thereby allowing the system to fully treat the contaminated fluid.
However, such upright/vertical orientation makes these systems undesirable for use in remote locations, because the upright vessel will often have to be transported in a horizontal orientation (e.g. to fit underneath bridges and to meet local vehicle and traffic regulations) and then be lifted or tilted upright from a transport vehicle to be installed at the remote location. For example, the current Commercial Vehicle Dimension and Weight Regulation under the Traffic Safety Act of the Province of Alberta, Canada sets the maximum width of a semi-truck, including any load, at 2.6 meters (approximately 8.53 feet) and sets the height of the highest point of the semi-truck, including any load, at 4.15 meters (approximately 16.6 feet) from the surface of the highway. The packing, porous media or contact cells may also not be suitable for use with crude oil and/or may be expensive to use and replace.
Finally, it is known that hydrogen sulfide contaminated water can may sometimes be treated through a process of air stripping. Air stripping typically occurs in an upright/vertical tower where the contaminated water is induced into the top of the tank and distributed over top of a layer of packing. The packing is designed to increase the surface area of the air-water interface, allowing a more complete volatilization. As the water descends, air is introduced separately from the water, near the bottom of the tank. The air then rises through the packing to stripping off the hydrogen sulfide. The water collects at the bottom with reduced hydrogen sulfide concentration and may exit through a sump. The hydrogen sulfide will then rise out of the top of the tank in a gaseous state. However, this type of air stripping is normally only suitable for contaminated water with lower concentrations of hydrogen sulfide, it may not work well with crude oil and typically results in the packing becoming plugged or contaminated. Often the water collected at the bottom of the tank will require further treatment to fully remove the hydrogen sulfide (e.g. with chlorination) and, if it works, it typically requires tall, upright vessels or towers with sufficient packing. Moreover, the use of packing complicates this system and adds to the cost, including ongoing operating material costs as packing needs to be replaced.
Therefore, what is needed is a simple, cost-effective apparatus, system and method to efficiently scrub contaminants such as hydrogen sulfide from fluids without introducing a chemical scavenger into the liquid portion of the contaminated fluid, without the need for packing, suitable for transport on the highways and without requiring complex and tall systems and apparatus. Preferably, and because the liquid portion of the fluid has commercial value (e.g. the liquid crude oil), the contaminant will be substantially removed from the liquid portion of such contaminated fluid, without requiring a secondary treatment for that liquid portion.